Polymers can generally be categorized as either thermoset polymers or thermoplastic polymers. Thermosets include polymers that are highly crosslinked and while they may exhibit some softening upon heating, they cannot be melted and reformed. While the lack of recyclability of thermosets is a detraction as is the fact that components formed of thermoset compositions cannot be welded to other materials, these components offer excellent physical characteristics including temperature and chemical resistance and dimensional stability as well as being very cost effective. Thermoplastic polymers exhibit a melting temperature and as such are capable of welding and recycling. In addition, they can exhibit higher impact resistance than thermosets and can also be highly resistant to chemical degradation. Unfortunately, thermoplastic polymers, particularly thermoplastic engineering polymers, can be quite expensive.
Composites that can incorporate both thermoplastic compositions and thermoset compositions could provide the desirable characteristics of both polymer types while mitigating the less desirable features. Unfortunately, primarily due to the difficulty in adhering thermoplastic components to thermoset components, it has proven very difficult to combine the two materials in formation of a stable composite structure. While improvements have been made in forming hybrid thermoset/thermoplastic composites, for instance through the utilization of epoxy-based blended polymers, such as toughened epoxies, the ability to form hybrid composite assemblies by use of thermoplastic zones in thermoset compotes and relatively quick and inexpensive processing techniques such as fusion bonding, has still not been achieved.
What are needed in the art are methods for formation of thermoset/thermoplastic composites and composites formed thereby. For instance, low cost hybrid thermoset/thermoplastic composites that exhibit the dimensional stability and resistance of thermosets while exhibiting the fusion welding capability of thermoplastics would be of great benefit.